This invention relates generally to steel making furnaces and the refractory linings thereof and more particularly to the repair of the refractory linings of top-charging electric furnaces.
The distinguishing feature of electric furnaces is the use of an electric arc to generate heat to melt and refine steel. The Heroult-type furnace is the dominant electric furnace. The furnace consists basically of a shell and refractory linings. The shell is cylindrical in shape, having a dome roof and a flat bottom. The bottom is lined with brick refractories, normally fireclay and silica or magnesite bricks, and a granular refractory is sintered into place over the refractory bricks to form the working bottom or hearth of the furnace. The cylindrical wall and the dome roof of the shell are also lined with refractory bricks, normally or silica. The dome roof and its refractory lining have a definite radius of curvature.
The furnace is mounted on toothed rockers which rest on and intermesh with toothed rails, and a motor rack-and-pinion mechanism can tilt the furnace in two directions, one for pouring and the other for slagging. A slagging door and a pouring spout are provided on opposite sides of the furnace. In the crown, or center, section of the dome roof, apertures for receiving electrodes, normally three, are provided and have water-cooled rings affixed thereover. The electrodes themselves are gripped by spring clamps affixed to the free ends of supporting arms, which arms are affixed to masts which raise or lower the arms and hence the electrodes.
Heroult electric furnaces are either door charging, a door for charging being provided in the side of the furnace, or top-charging, the dome roof being lifted and either swung to one side by motor-driven or hydraulic equipment or moved away by a gantry crane which travels on rails. We are here concerned with top-charging electric furnaces.
After the furnace has been charged, the dome roof is swung back over the furnace. The electrodes are lowered by the masts, through the apertures in the dome roof, to project into the interior of the furnace. The furnace is actuated, and current arcs directly from one electrode, into the metal or bath, therefrom to a second electrode, back into the bath, and then to a third electrode, in what is known as a direct-series arc. After the particular steelmaking process has been completed, the electrodes are raised, the power turned off, and the steel tapped into ladles. Thereafter, before the next heat, the dome roof is swung outwardly from the furnace, and the refractory lining of the roof is checked. Repair patching of the lining is done immediately to allow the refractory patching material to be sintered into place by the heat of the furnace.
The roof of an electric furnace is subjected to very high temperatures and great abrasion. Particularly severe localized high temperatures and corrosion or erosion occur in the crown section, through which the electrodes penetrate the furnace. High alumina refractory bricks have been developed for use in the crown section such that the life of the crown section more nearly approximates that of the rest of the roof lining. Nevertheless, the roof lining of the electric arc furnaces must still be attended to between heats to ensure a reasonable lifetime for the lining. A fast and efficient way of doing this has not been developed, the structures which have been developed so far for spraying refractory coating being adapted for use with concentric types of vessels, having an open end, known as basic oxygen furnaces.